1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device applicable to so-called one-chip full-color liquid crystal display panels such as microlens-integrated liquid crystal display devices without a color filter.
2. Related Background Art
The world of today is in the age of multimedia, and equipment for communication by image information is becoming more and more important. Among others, the liquid crystal display devices are drawing attention because of their slimness and low power consumption and have grown to one of basic industries comparable to the semiconductors. The liquid crystal display devices are mainly used for 10-inch notebook-size personal computers at present. It is expected that the liquid crystal display devices of larger screen sizes will be used not only for the personal computers, but also for workstations and televisions for home use in future. With increase in the screen size, however, manufacturing equipment becomes expensive and, in addition, electrically exacting characteristics are demanded for driving of such large screens. The manufacturing cost will thus increase abruptly in proportion to the square to cube of the size with increasing screen size.
Recently, attention is thus drawn to a projection method for preparing a compact liquid crystal display panel and optically enlarging a liquid-crystal image to display an enlarged image. This is because the microstructure tendency of semiconductors permits decrease in the size, improvement in the characteristics, and decrease in the cost, similar to the scaling rule to improve performance and cost. From these aspects, in the case of the liquid crystal display panel of the TFT type, TFTs have to be compact and have sufficient driving force, and transition is now occurring from the TFTs using amorphous Si to those using polycrystal Si. Video signals of the resolution level conforming to the NTSC system etc. used in the ordinary televisions do not require so quick processing.
This allows not only the TFTs but also peripheral driving circuits such as shift registers or decoders to be made of polycrystal Si, whereby the liquid crystal display devices can be constructed in monolithic structure of a display region and a peripheral driving circuit region. Polycrystal Si is inferior to single-crystal Si, however. For realizing high-definition televisions having the higher resolution level than the NTSC system or display of the XGA (extended Graphics Array) or SXGA (Super extended Graphics Array) class in the resolution standards for computers by polycrystal Si, a shift register needs to be composed of a plurality of segments. In this case, noise, called ghost, appears in the display region at portions corresponding to borders between the segments and there are desires for a solution to this problem in this field.
On the other hand, focus is also drawn to display devices using a single-crystal Si substrate, which can realize extremely higher driving force than the display devices of the monolithic structure of polycrystal Si. In this case, the transistors of the peripheral driving circuitry have sufficient driving force and thus the divisional driving described above is not necessary. This solves the problem of the noise and the like.
A microlens-integrated liquid crystal panel and a projection-type liquid crystal display device using it are disclosed in Japanese Laid-Open Patent Application No. 8-114780, for example. The microlens-integrated liquid crystal panel in this case is normally of the transmission type and it was constructed in the structure as illustrated in FIG. 13. Specifically, illumination beams of the respective primary colors of R, G, and B are guided at mutually different angles onto the liquid crystal panel and then onto pixels 1318 different from each other by converging action of microlenses 1316. This eliminated the need for the color filter and enabled to achieve high light utilization efficiency. The projection type display device of this type can project and display a bright full-color picture even by use of the one-chip liquid crystal panel which is a single liquid crystal panel capable of creating the colors R, G, B. Such projection type display devices are gradually becoming commercially available.
On the other hand, various attempts have been made to achieve operational modes of liquid crystal of the liquid crystal panel used in the liquid crystal display apparatus, and there are operational modes including a mode using ferroelectric liquid crystal, a TN mode using nematic liquid crystal, which is relatively popularly used, an STN mode, an IPS (In-Plain-Switching) mode, a polymer-dispersed liquid crystal mode, and an electrically controlled birefringence (ECB) mode for controlling birefringence of liquid crystal cell by application of an electric field. As for the ECB mode, there are three types of methods, among which the DAP (deformation of vertical aligned phase) type uses the nematic liquid crystal having negative dielectric anisotropy. Namely, the liquid crystal in the initial state is in vertical alignment (homeotropic alignment) and the liquid crystal molecules become inclined with application of voltage to change incident, linearly polarized light into elliptically polarized light by the birefringence effect, thereby achieving gradation display. This method has steep voltage-reflectance characteristics and black is easy to create in the normally black mode by use of orthogonal polarizers. Therefore, this method can implement high-contrast liquid crystal display.
For use of the liquid crystal apparatus of the DAP mode, it is important to uniformly align longitudinal axes of liquid crystal molecules with the vertical direction to the substrate in the initial stage and how uniformly and stably angles and directions of pretilt of the molecules are controlled would be a key to enhancing the contrast and in-plane uniformity which represent the performance of the liquid crystal display apparatus. A method known for implementing such vertical alignment is, for example, application of such an amphiphilic surface-active agent as lecithin or organic silane (Liquid crystal-applications, p61, coauthored by Koji Okano and Shunsuke Kobayashi, Baifukan).
A variety of oblique evaporation methods and rubbing methods are normally used as methods for controlling the pretilt angles of liquid crystal molecules at elevations of about 1 to 5 degrees relative to an alignment layer surface, and there is also a recent report to suggest a method for controlling alignment by irradiating the vertical alignment layer with ultraviolet rays. Among these the rubbing methods are techniques excellent in mass productivity and cost efficiency, which are often used in practice.
The vertical alignment layers, however, still have the problems that their wettability is poor, that it is hard to form the layers stably in uniform thickness and quality of film, and it is hard to implement reliable control of alignment. Particularly, there are some cases in which display characteristics are degraded considerably by disturbance of alignment caused by weakness of adhesion of the alignment layers at step portions of base layer in contact with the alignment layers. In particular there is a possibility that the problem becomes significant on the occasion of rubbing for the pretilt control.
Further, in the case of the microlens-integrated liquid crystal panels, say the conventional example described above (FIG. 13), a projection display image thereof is an enlarged projection image of the pixels 1318 of R, G, and B on the screen and, therefore, the mosaic pattern of R, G, and B becomes prominent as illustrated in FIG. 14. This could degrade the quality of display image.
An object of the present invention is to provide a liquid crystal display device that can be applied to the one-chip projection type liquid crystal display apparatus and that can display a full-color projection image color-mixed in each pixel without the mosaic pattern.
Another object of the present invention is to provide a liquid crystal display device that can achieve high-contrast display in the DAP mode having the vertical alignment layers of polyimide with stable alignment characteristics.
Another object of the present invention is to provide a liquid crystal display device comprising a matrix substrate in which a plurality of pixel electrodes are arrayed in a matrix pattern in correspondence to colors of R (Red), G (Green), and B (Blue), an opposite substrate in which an opposite electrode is placed opposite to said pixel electrodes, and a liquid crystal material having negative dielectric anisotropy, the liquid crystal material being placed between the matrix substrate and the opposite substrate, wherein there are provided an alignment layer of polyimide with a vertical alignment property and a microlens array having a plurality of microlenses, and wherein the microlenses are provided at a pitch of two pixels relative to an array of the pixel electrodes.
The present invention embraces such a configuration that in an array of basic pixels of R, G, and B in a color-filter-less reflective liquid crystal panel, the color pixels are arrayed so that mutually different combinations of two colors out of the these three primary color pixels are arranged in a first direction and in a second direction different therefrom, a two-dimensional microlens array has microlenses at the pitch of two pixels relative to the pixel array, the first primary color pixels out of the colors R, G, B are located at positions corresponding to centers of the microlenses, the second primary color pixels are located at positions corresponding to borders between adjacent microlenses in the first direction of lines of the microlenses, the third primary color pixels are located at positions corresponding to borders between adjacent microlenses in the second direction of lines of the microlenses, a first primary color beam is made incident from a direction normal to the reflective liquid crystal panel, a second primary color beam is made incident thereto as inclined relative to the normal direction toward the first direction, and a third primary color beam is made incident thereto as inclined relative to the normal direction toward the second direction, so as to illuminate the liquid crystal panel.
In this configuration, the above illumination system is so set that the first primary color beam incident through a microlens onto a first primary color pixel is reflected thereby to return in the same optical path, while the second or third primary color beam incident obliquely through a certain microlens onto a second or third primary color pixel is reflected by the pixel located at the border of the microlens and is emergent from a microlens adjacent thereto. In connection therewith, it is preferable to select a combination of each set of R, G, and B pixels composing each picture element against each microlens position as follows. In each of the second and third primary color pixels, a pixel selected is one located in the direction of incidence of the illumination light out of the two pixels adjacent to the first primary color pixel and so selected pixels of the second and third primary colors are combined with the aforementioned first primary color pixel. Reflected beams of the respective primary colors from each set of R, G, and B pixels are modulated by the liquid crystal and thereafter are emitted through the same microlens.
When especially this microlens position in the liquid crystal panel is projected and imaged on the screen by a projecting means such as a lens, an image is projected through the modulation of the liquid crystal panel in a macroscopic sense and the R, G, B pixel images from each pixel are projected in a color-mixed state as a superimposed image in a microscopic sense.
Further, when the surface of the above active matrix substrate is flattened, the vertical alignment layer can be formed stably and the liquid crystal display device can be constructed with high contrast.
Further, the vertical alignment film may be formed in multilayer structure, in which a layer on a base metal electrode layer is a layer with high adhesion and high wettability to the base metal electrode layer and in which the outermost surface layer in contact with the liquid crystal has low surface energy. This structure permits formation of the liquid crystal panel of the DAP mode with high reliability but with little peeled-off layer, in which alignment of the liquid crystal is vertical and in which angles of pretilt are uniform.